SKG-3a and SKG-3b are two distinct human uterine cervical epidermoid carcinoma cell lines derived from a single donor. We studied these two closely related cell lines from the standpoint of drug susceptibility. The growth inhibitory effects of cisplatin (CDDP), doxorubicin (ADM), etoposide (VP-16), and paclitaxel (taxol) on SKG-3a and SKG-3b cells assessed by crystalviolet dye uptake assay were almost the same. SKG-3b cells treated with CDDP, ADM, VP-16, and taxol showed the apoptotic cell death, whereas apoptosis in SKG-3a cells was not induced by these anticancer drugs. Caspase-3 activity was increased only in the SKG-3b cell lysate after treatment with CDDP, ADM, and VP-16 but was not found in the SKG-3a cell lysate. These results indicate that despite growth inhibitory effects of anticancer drugs being almost the same, there may be differences in the common signaling pathways involved in the apoptotic process between SKG-3a and SKG-3b obtained from the same tumor.